


apex predator

by jaemarked



Category: NCT (Band)
Genre: Alternate Universe - Merpeople, Established Relationship, Explicit Sexual Content, Fluff, Humor, M/M, Minor Injuries, Plot What Plot/Porn Without Plot, Porn with Feelings, Science Fiction, Semi-Public Sex, Smut, Tentacle Sex, Tentacles, Water Sex, merman!jaemin, minor description of a shark attack
Language: English
Status: Completed
Published: 2020-08-10
Updated: 2020-08-10
Packaged: 2021-03-05 22:40:57
Rating: Explicit
Warnings: No Archive Warnings Apply
Chapters: 1
Words: 5,149
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/25812958
Author URL: https://archiveofourown.org/users/jaemarked/pseuds/jaemarked
Summary: “You planned for this,” Mark accused.“I did,” Jaemin replied. “Do you wanna fuck here or on the beach?”Jaemin was so crude sometimes.
Relationships: Mark Lee/Na Jaemin
Comments: 8
Kudos: 187
Collections: Mark Lee Birthday Bash 2020





	apex predator

**Author's Note:**

  * For [TRASHCAKE](https://archiveofourown.org/users/TRASHCAKE/gifts).



> happy belated mark lee day!
> 
> this is far, far different from anything i usually write but i found that i actually quite enjoyed it. thank you to my prompter who challenged me write something i had to do a lot of questionable research on. as it is, i don't know anything about marine biology so i apologize if this is inaccurate.
> 
> also, while we're here, happy birthday jaemin! 
> 
> CONTENT WARNING FOR: mentions of a shark attack, sex in a cave, WEIRD MERMAN ANATOMY AS IN JAEMIN HAS TWO TENTACLE LIKE DICKS

“Identification number?”

“990802,” Mark replied to the security AI. The surface of the door shimmered and a panel appeared. 

“Passcode, please,” the AI’s pleasant voice commanded. Mark reached over and keyed in his sixteen digit password, then pressed his thumb against the fingerprint scanner that popped up next. Finally, he leaned over and looked straight into the iris scanner. Green light flashed over his face and the door beeped, the light above changing from red to green.

“Welcome back, Dr. Lee,” the security AI said, and Mark pushed open the door with his hand. The lab’s unnerving white walls lined with LED strip lights were the first thing that greeted him, but he strode confidently down the hall, pulling on his cream overcoat that had been hanging over his elbow. They didn’t use white lab coats here. 

He stepped into the elevator, pushing the button for B15, fifteen floors below sea level. It wasn’t the furthest he could go, but it was as far as he needed to. The halls that greeted him when he stepped out were not gleaming white. They were made of glass, and they allowed him to see into the ocean beyond. There was a chocolate pipefish right next to the glass, and Mark paused to watch it swim by before continuing on his way.

The Neo Technology Marine Life Institute was a research facility in the middle of the Pacific Ocean, on a man-made private island called Suh Island. It belonged to billionaire and CEO, Johnny Suh. Mark was the head of the research team and had just come back from an extended health break. The reason for his break was rather obvious -- he clenched his fist and flexible titanium alloy and carbon fibre bent to his will. He still wasn’t used to it after six months of physiotherapy, but it was fine. He had time. In fact now that he was at NTMLI, he had nothing _but_ time. Accessible only by boat or helicopter, the NTMLI was completely isolated. Except for him, his scientists, and some of the staff, there was no one else for miles. Once a month, a supply boat would come and drop off a shipment of everything they needed. 

“Dr. Lee, welcome back!” Jaehyun, one of the scientists at the Institute, greeted him. 

“Thank you, I’m glad to be back,” Mark replied, “but you know you can just call me Mark, right?”

“Right, right, I guess I forgot,” Jaehyun replied sheepishly, his dimples popping as he smiled. When Mark first met him two years ago, he thought Jaehyun was more suited to be a model than a researcher — that was until he read Jaehyun’s paper on _exocoetus peruvianus,_ better known as Peruvian flying fish. Mark had stolen Jaehyun from the Smithsonian Tropical Institute, and now he was on Mark’s team. 

“Where’s Doyoung?” Mark asked. “And Taeyong?” The lab was void of his famous duo, a pair of married scientists known for their groundbreaking research in new underwater camera lenses, as well as their joint paper on the dietary habits of the _percis japonica_. 

“They’re down in Titania’s Arch with the girls,” Jaehyun answered, plopping down in his seat in front of the monitors. 

“And Jaemin?” 

Jaehyun didn’t even look, jerking his thumb over his shoulder at the window that took up the entire south wall of the lab, made of a hybrid polycarbonate glass that was practically indestructible. Mark turned around to see Jaemin zoom past like a torpedo cutting through the water. He didn’t even see Jaemin look through the window, but he circled back, eyes lighting up when he caught Mark through the glass. 

It had been six months since they last saw each other, and Jaemin was as beautiful as ever. His hair was a dark blue, matching the blue scales of his tail that faded into black towards the end of his fins. His skin was tanned golden, probably from hours spent lounging in the sun. But nothing was more beautiful than the smile on his face when he realized that Mark was _back._

Jaemin pointed up, and despite the fact that Mark had just gotten here, he abandoned everything to sprint to the elevator, taking it back to ground level and immediately running out onto the docks. Sure enough, Jaemin was waiting for him, his arms folded on the wood and a beatific grin plastered on his face, his wet hair pushed off of his forehead. 

“Hi,” Mark greeted, dropping to his knees on the wet dock. 

“Hello,” Jaemin replied. “You’re back.”

“I am,” Mark agreed. His face hurt from how much he was smiling. 

“So, let me see it,” Jaemin said. Mark sighed, but he indulgently pulled his arm out of his coat and presented it to Jaemin, who immediately began marveling over the technology. He ran his hands along the part where the metal seamlessly blended into Mark’s skin. “Does it still hurt?”

“Sometimes,” Mark admitted, “but it’s better than my first model.”

The hospital had given him a temporary prosthetic hand after the accident, before Johnny had his custom one made. It had been horrible, but luckily he hadn’t used it for long. His new one was much better, and came with built-in tech that would help Mark on his dives, as soon as he was cleared to go on them again.

“I’m really sorry, Mark,” Jaemin whispered, and Mark almost didn’t hear it over the sound of waves against the support beams of the dock. 

“Why?” Mark asked, completely mystified. None of it had been Jaemin’s fault. 

“Will you dive with me?” Jaemin suddenly asked. Mark didn’t miss that he was trying to avoid answering his question, but he chose to ignore the obvious change in topic. 

He hesitated. “I dunno if I should, I’m not cleared yet--”

“Please,” Jaemin begged, his dark eyes shining. “It’s been so long.”

Mark looked at his hand once more. It should be fine, his wetsuit would cover it and prevent it from getting damaged, and of course his prosthetic and its tech were completely waterproof. He’d even gone scuba diving several times during his vacation as part of his physiotherapy as well as exposure therapy. He was completely safe -- in theory.

But even though it had been more than six months ago, and Mark’s recovery was extraordinarily speedy, the accident was still fresh in his mind. And it _was_ an accident -- it had been no one’s fault. The system of Mark’s mini submarine had malfunctioned, he had crashed, and he was bleeding in deep waters. Jaemin had immediately come to save him, but not before a shark had come for his arm. If Jaemin hadn’t come in time, he wouldn’t have survived at all. 

The strongest creatures in the sea were not sharks or whales or dolphins — they were mercreatures. 

“Okay,” Mark told him, “let’s dive.”

Jaemin squealed happily, and Mark went to get his wetsuit. They definitely weren’t going far — Mark wasn’t ready to be away from the Institute, but he still prepared with all the latest gear that Johnny had acquired. His new wetsuit was made from foamed neoprene and a hybrid lycra that maximized thermal insulation and buoyancy. It was like a second skin to him, as familiar as the back of his hand, and pretty soon he had his mask on, jumping into the water and splashing Jaemin. 

“We’re staying near the surface,” Mark said, and Jaemin immediately agreed. Diving with a merman honestly didn’t require much, especially not with the new technology Mark had on him, but he still liked to be prepared. Jaemin latched onto him as soon as he was in the water, his arms around Mark’s neck. Mark immediately wound his arms around Jaemin’s waist, at the spot where scales met skin. Jaemin’s skin felt different from human skin; it was harder and less fragile, but smooth to the touch. Mark’s blunt human nails couldn’t scratch them — and he’s tried.

Jaemin took him under the water, his powerful tail propelling them through the sea faster than Mark could ever swim. When they stopped, it was further from the surface than he liked, but he wasn’t going to say anything, not when Jaemin looked so happy. He wished he didn’t have to wear a mask strapped to a tank. He wanted to smile back. But unfortunately, he wasn’t like Jaemin, and he couldn’t breathe underwater. 

He wanted to go to Titania’s Arch. The underwater city where Jaemin’s people lived. But it was so far below the surface, and from the NTMLI. The distance was practically nothing to Jaemin, who could swim at speeds higher than 68 mph, faster than a sailfish. He could get to Titania’s Arch in minutes, and he could take Mark with him.

But even though Mark had been diving all his life, had learned to swim almost immediately after he learned to walk, and was part of the best marine life research team in the world, he was still afraid to go deeper. Even with an apex predator at his side. 

Jaemin suddenly grabbed him by the arm and took him back up to the surface, and Mark just went along with it. He went along with anything Jaemin did, because he had never been capable of saying no. Not since the first time they met, more than two years ago. Jaemin had almost killed Mark, but only because he was afraid that Mark would kill him first. Or worse.

They had come so far, and Mark thought about it as they broke through the surface, bobbing in the water only about a mile away from the Institute. 

“I changed my mind,” Jaemin said when Mark gave him a questioning look. “I want to take you somewhere.” 

“Sure,” Mark agreed, though he had no idea where Jaemin was planning on taking him. 

“Wanna take a boat? Or do you wanna swim with me?” Jaemin asked. 

“How far is it?” Mark wondered, and Jaemin gave him a sheepish smile. 

“I forget you can’t swim long distances,” Jaemin said apologetically. “Okay, let’s get you in a boat.” 

Mark’s boat wasn’t necessarily a boat. It was more like a jet-ski, but high-tech and had protective walls that made it _look_ like a boat. Doyoung called them water riders, Taeyong thought that was a stupid name, and Jaemin thought everything was a boat and couldn’t be convinced otherwise. It was used for surface-level solo expeditions, but they had six of them, so it wouldn’t matter if Mark borrowed one for a few hours. He typed in his passcode and scanned his thumb, and began following Jaemin. He could tell Jaemin was getting frustrated with the slow speed, but it was a nice day out and Mark appreciated being outdoors. His arm was starting to ache a little, but he ignored it. He had missed this, missed Jaemin. He could put up with it for a while longer.

“Where are you taking me?” Mark asked with a laugh. Jaemin grinned and pointed at an island that was beginning to appear on the horizon, then sped up, swimming ahead of Mark’s boat. 

Mark followed him to the island and to a secluded cove. Jaemin made him abandon his boat, his mask, and his wetsuit, and jump into the water, and with his help they swam into a cave, narrow at first but then opening up to an underground pool. The top of the cave had a hole like a skylight, allowing the sunlight to stream in and illuminate the limestone walls.

“Oh, Jaemin,” Mark breathed, “it’s beautiful. How did you find this place?”

“Lots of exploring,” Jaemin said with a grin, now swimming on his back. “I’ve been going out every day.”

Sometimes, Mark wanted to beg Jaemin to stay in Titania’s Arch, or even at the Institute, where he would be safe from humans who might try to capture him and sell him for a hefty price. But it would be too selfish for him to ask, and so he kept his mouth shut and listened as Jaemin chattered away about the different places he explored. 

“What?” Jaemin said, giving Mark a weird look, and Mark realized he had just been staring with a creepy grin on his face. He winced, his face burning despite the cool temperature in the cave.

“Sorry I just… I just missed you,” Mark confessed. “I wasn’t allowed to v-call the Institute, it was part of my therapy, but I missed you so much.”

“I missed you too.” Jaemin’s eyes were soft and dark, sparkling in the sunlight, and Mark was instantly reminded of a baby weddell seal. “How’s your arm?”

“What?” Mark glanced at his hand, though it was covered by his wetsuit. “Oh, it’s fine.”

Jaemin didn’t look convinced.

“Seriously, Jaem, it barely even hurts,” Mark assured him. He hesitated, then said, “you know it wasn’t your fault, right?”

“It was,” Jaemin whispered, “I _knew_ there was a hostile shark in the area, I should have killed it when I had the chance—“

“Jaem, I was bleeding in the water,” Mark cut him off. “It thought I was an animal and it took a bite out of me. If anything, it was my fault for soloing.”

“How were you supposed to _know_ the system had a bug?” Jaemin looked like he was going to cry. “I should have been faster responding to your distress signal, I should have—“

“You saved my _life,_ ” Mark said, “and you single handedly fought a great white shark and _won._ ” 

“About that,” Jaemin said nervously, “I don’t think that was a great white.”

Mark stared at him. “What do you mean?”

“Doyoung and Taeyong said that it was definitely in genus _Carcharodon,_ but not _carcharias,_ ” Jaemin explained. “Actually, they said they can’t be too sure, since all that was left…”

…were some teeth. Jaemin hadn’t shown mercy.

“Well, anyway,” Jaemin continued, “they said that… it could have been a new species.”

“No _way,_ ” Mark breathed. He couldn’t believe his ears. “A new species?”

“Don’t get your hopes up,” Jaemin warned, “it might just be a fluke.” 

“Still,” Mark said excitedly, throwing his arms around Jaemin’s neck, “even the possibility is amazing.”

“ _You’re_ amazing,” Jaemin replied, eyes curving into crescents with the force of his smile. Mark’s gaze flickered down to his lips for just a brief moment, but a moment was all it took. He didn’t know which of them moved first but suddenly they were kissing, Jaemin’s cool lips against Mark’s hot mouth. Jaemin thrust his tail, and propelled Mark backwards until his back was pressed against cool, flat stone. It was smooth to the touch, and didn’t scratch up his back. Of course, Jaemin would have the foresight to think about those kinds of things.

Mark parted his lips, felt Jaemin’s tongue against his teeth and gasped, heat coiling in the pit of his belly. He tightened his grip on Jaemin and pulled him closer. Jaemin pressed him up against the wall until his feet couldn’t touch the bottom of the pool, and he wrapped his legs around Jaemin’s waist. 

“Jaemin,” Mark gasped when Jaemin’s mouth moved down to his neck, his sharp teeth digging into his flesh without puncturing his skin. A shiver ran down Mark’s spine — Jaemin could kill him right now, if he wanted to. 

But the way Jaemin was kissing his neck showed he didn’t want to. 

“I missed this,” Jaemin murmured, sucking a bruise just below Mark’s collarbone. He lowered Mark back into the water and pulled off his shirt, the wet fabric getting caught in Mark’s hair. They laughed as they struggled to get it off together, and once it was finally off, Jaemin tossed it onto 

a ledge protruding from the cave wall and then pounced, running his hands all over Mark’s torso. “Mark, I want you.”

“Jaemin…”

“Please,” Jaemin whined, pushing closer in the water. Mark’s hands rested on his tail, below where his hips would be, petting soothingly at his scales. 

“Not here, we don’t have anything.” Lube, specifically. 

“There’s some in your boat,” Jaemin said gleefully. 

“You planned for this,” Mark accused.

“I did,” Jaemin replied. “Do you wanna fuck here or on the beach?” 

Jaemin was so crude sometimes. 

“Here’s fine, I’m not looking to get sand up my asscrack,” Mark replied. 

Jaemin wrinkled his nose. “Mark, you can be so crude sometimes.”

“Pot, meet kettle,” Mark said, but Jaemin just gave him a confused look and swam away. He didn’t really understand human idioms, but to be fair Mark didn’t understand merpeople idioms either. 

He swam over to the flat bed of rock at the end of the cave and pulled himself out of the water. The sun was shining right on the rock, making it warm beneath his back and helping to dry him off. He could hardly believe they were going to fuck in a cave, but then again they’ve had sex in worse places. The docks at the Institute, for one.

“Where did you get this?” Mark asked when Jaemin returned with a bottle of waterproof silicone lube. There was only one answer — he got it from someone at the Institute. “Oh god, Jaem, who did you ask for this?”

He hoped it wasn’t Jaehyun. He would be teased for _weeks._

“Taeyong gave it to me,” Jaemin said with a grin, swimming up to the bank and folding his arms on the rock, staring up at Mark like he was something precious. “He also gave me a lecture about the human body and how delicate you guys are.” 

Mark’s face was burning. He could imagine Taeyong’s rants, and figured he was going to be in for a lecture of his own when he returned. “Oh my god.”

“Don’t worry, I did a lot of research.” Jaemin looked absolutely delighted. “It was all very scientific, I promise.”

“Research?” Mark asked warily.

Jaemin propped himself up on the rock, his tail splashing in the water as he leaned in close to whisper conspiratorially in Mark’s ear. “ _Pornography.”_

Mark grabbed Jaemin’s face and shoved him back into the water. Jaemin resurfaced with a giggle, using his tail to spray Mark in the face, then climbed back onto the rock to pull off the rest of Mark’s clothes. 

“Sorry we can’t do this in a bed,” Jaemin said, sounding guilty.

Mark blinked. “What? We’ve never done this in a bed.”

“Exactly.” Jaemin pouted. “I wish I had legs or something.”

“Nah, you wouldn’t be you if you didn’t have your tail,” Mark replied. 

“You’re right,” Jaemin said with a grin, “and it’s _me_ you find sexy.” 

_Aaaand he’s back_.

“I do,” was all Mark said before he hooked his arms around Jaemin’s neck and pulled him in for a kiss. He wrapped his legs around Jaemin’s legs once more, ankles crossed at the small of Jaemin’s back. 

“Come back in the water,” Jaemin whined. 

“Jaem, if you want to fuck me, we can’t spend all our time kissing,” Mark teased.

“Yes, we can,” Jaemin said sulkily, but he backed off. Mark sighed, reaching for the bottle of lube that Jaemin brought. He wasn’t really a fan of fingering himself, but he didn’t have the time to teach Jaemin today.

When they had sex, it was usually non-penetrative, or Mark topping. But he’d seen what Jaemin was working with and he had to admit he was… intrigued.

Or maybe he was a bit of a size queen.

He took his time, aware of Jaemin watching him. His ears burned when he circled his rim with one finger, Jaemin’s stare boring into him. 

“Does it feel good?” Jaemin asked. 

“Hmm, not really,” Mark replied, pushing his finger in, trying not to clench down. It had been a while since he’d done this. “It mostly just feels weird.”

“Like that time I got a puffer fish spine stuck in my tail fin?” Jaemin asked. Mark stared at him, but he was completely serious. 

“Sure,” Mark deadpanned, adding more lube and pushing in another finger. 

Jaemin gasped. “Isn’t it too soon for two?”

“I’m fine,” Mark assured him, laughing a little when Jaemin splashed his tail, clearly distressed. “Humans are delicate, but they’re not _that_ delicate.”

“Your orifice is made of delicate tissue,” Jaemin observed.

Mark grimaced. “Can’t you just call it an asshole like everyone else?”

“Can I try?” Mark sighed and nodded, passing the lube to Jaemin. He didn’t really need more, but it was better for Jaemin to get into the practice of using it, since his own kind did not. From what he knew, all merpeople were self-lubricating. Jaemin specifically had what he called a “slit” in his tail where his genitalia was located. Mark had fucked into that slit before, had pressed his fingers and his cock inside, but he’d never _been_ fucked by Jaemin before. “How do I do it?” 

“Start with one finger,” Mark instructed, “just push in gently, like this.” 

“I think I’m better at blowjobs,” Jaemin sighed, but he obediently pressed a finger past the tight circle of muscle. Mark took a deep breath and forced himself to relax as Jaemin wiggled his finger around. “This is fun, can I put another?”

_Fun?_

“Sure, but go slow.” He didn’t think Jaemin would take him so literally, but by the time he sank another finger inside, Mark’s hips were twitching impatiently as he tried to not grind down on Jaemin’s fingers. “Jaem, you’ve gotta move.”

“What if I hurt you?” 

Mark sighed and reached to cup Jaemin’s face with his clean hand. “Baby, you’re not gonna hurt me, okay? Trust yourself, and if you can’t, then trust me. I’ll guide you. But you gotta move or I’ll go crazy.” 

“Okay.” Jaemin’s tongue poked out from between his lips in concentration as he twisted his fingers, pushing them in deeper, the lube squelching and making him giggle. Mark rolled his eyes, but tweaked Jaemin’s ear, then gasped when Jaemin jammed his fingers in harder as revenge, brushing against his prostate. “Hey, there’s something spongy here.”

Mark let out a disbelieving laugh, gritting his teeth when Jaemin deliberately stroked his prostate. He was just curious, but he clearly had no idea of the effect it was having on Mark. 

“Does this feel good?” Jaemin asked when Mark’s hips buckled wildly.

“Yes,” Mark gasped, “Jaem, Jaem, stop. Too much.”

“Sorry!” Jaemin cried, carefully pulling his fingers out. 

“It’s okay,” Mark breathed, “just, um, I didn’t want to come too soon, or else this would be over pretty fast.”

Jaemin pouted. “I like when you do.”

“I know,” Mark groaned, remembering the time in the Institute pool when Jaemin had made him come _three_ times. He had slept for thirteen hours after that. “Not this time, okay?”

“Okay.” Jaemin withdrew with a pout, and Mark immediately pushed three fingers inside himself. It stung a little, but he adjusted to it quickly enough, panting as he spread them to stretch himself out. 

“Come here,” Mark instructed, and Jaemin pushed himself up out of the water, his arms on either side of Mark as he bent his head to kiss him. 

“Are you ready now?” Jaemin murmured against his lips.

Probably not, actually, but whatever. Mark had done worse with less. He slipped off of the rock and into the water, gasping when he was immediately spun around, his front pressed against the stone. His fingers scrabbled for purchase, tightening around notches in the rock. 

Jaemin groped at his ass, hitching him up higher. Mark shivered at the blatant display of strength, his chest pressed against cold rock as Jaemin’s dick slid along his crack, secreting some kind of viscous liquid that gave away his arousal.

He’d seen Jaemin’s dick before. Or, rather, his _dicks,_ two long, thin appendages, dark blue and covered in hard ridges and nubs. Mark was going to _die,_ and he fully anticipated it.

“Jaemin,” Mark gasped, “stop teasing.”

Jaemin chuckled lowly, but one of his dicks probed at Mark’s entrance, rubbing against his rim. Mark clenched involuntarily, shaking, and gasped when Jaemin slowly pressed in, aided by the lube and his own secretion. 

The first ring of nubs caught on the edge of Mark’s rim and he choked out a moan as Jaemin kept pressing forward until they slipped in. 

“Wait, wait,” Mark gasped, and Jaemin instantly paused. “Let me adjust.”

He felt like a tightly wound up spring, or maybe a balloon ready to burst. His ass ached already, Jaemin’s size more than he was used to. He got pretty adventurous with toys, but not for six months while he was away from his bedroom at the Institute.

 _Wait._ Mark froze. _Had anyone cleaned his room while he was gone? Please tell me nobody looked in my drawer. I would die of embarrassment._

Jaemin grunted behind him, and slid an inch deeper, pressing against Mark’s prostate. Mark’s eyes rolled to the back of his head and he nearly slipped off the rock, heat flaring in his abdomen. 

“ _God,_ ” Mark gasped. “There, Jaemin, harder, faster, _anything._ Just _please—“_ he choked out another moan as Jaemin slammed in further, rocking his body upwards as his dick punched in deeper, his other dick sliding between Mark’s thighs, pressing against his balls and the length of his cock. Mark cried out, muffling it with his hand as Jaemin pounded into his ass. The texture was unlike anything Mark had ever felt before, scraping inside of him and catching at his rim. 

“Mark,” Jaemin whined, pressing his chest to Mark’s back, his teeth closing around Mark’s ear. He shuddered, pressing his hips back as best as he could while still being pinned to the rock. Jaemin’s arm slid around his neck, hiking him up backwards until he was practically upright, his arms propping him up off the rock as Jaemin sunk in even deeper. Mark wanted to scream, wanted to turn around and see how much was left, but Jaemin wouldn’t let him move, his other arm wrapping around Mark’s waist.

“Fuck,” Mark spat, and felt sharp, pleasure-pain when Jaemin pressed his hand against his abdomen. He was so fucking full. He was going to die here, getting fucked by Jaemin, so delirious he could barely see the cave walls around him. Drool dripped from his mouth when Jaemin sped up, but he couldn’t figure out how to close it.

He felt Jaemin push in deeper still, so much that he wondered if he could feel it in his guts. When he looked down, he gasped when he noticed the small bulge in his normally flat stomach, half hidden by Jaemin’s hand.

“Oh, fuck,” Mark moaned, and came, his toes curling in the water and his head dropping back against Jaemin’s shoulder. His vision whited out, and he distantly felt Jaemin’s second dick rubbing his own as Jaemin stilled his hips, pressing against Mark’s prostate and prolonging his orgasm. 

“Mark, Mark, Mark,” Jaemin chanted his name desperately, thrusting erratically as he chased his own release. The overstimulation was bringing tears to Mark’s eyes, and soon he was full out sobbing while Jaemin pounded away at his ass. He was beginning to ache something fierce, and his arms were definitely going to bruise from being pressed against the rock. Suddenly Jaemin’s hips stilled and Mark felt his dick throb inside of him, his only warning before Jaemin was pumping his semen inside of him and all over his thighs, his second cock spurting all over the rock in front of Mark, splattering over his spent cock.

There was so much of it, filling Mark’s stomach and dripping out of his ass still stretched around Jaemin’s dick. He felt Jaemin extract from between his thighs, then slowly pulling out of Mark’s ass, leaving him clenching around nothing. Only a few seconds passed before Jaemin spun him around, yanking him down into the water and kissing him desperately, all lips and teeth and tongue, licking up the drool from Mark’s chin and making the most obscene noises.

“Thank you, thank you,” Jaemin was saying, and Mark’s brain, turned to mush, tried to make sense of it as he went limp in Jaemin’s arms. Jaemin had no trouble keeping them both afloat, laying on his back and pulling Mark on top of him like he was a raft. He felt fingers probing at his rim again, pushing inside to scoop out his come. “It’s all messy in here.”

Mark pulled a face. “Do you have to be so crass?”

He shivered when Jaemin pressed up against his prostate, his dick stirring despite the fact that he just came, and he quickly shoved at Jaemin’s shoulder. “Dude, no way can I go again. I think you broke me.”

Jaemin just laughed and finished helping Mark clean up, then lifted him back onto the rock so he could get dressed. It was getting colder now, and they needed to get back to the Institute before it got dark. Mark was aching all over, but it was good, and he was still practically on cloud nine. Jaemin looked extremely pleased with himself.

“I’m gonna need you to help me get back to the boat,” Mark admitted when his knees buckled. Jaemin tugged him down into the water and wrapped an arm around his waist, swimming out of the cave to where Mark had left his boat on the beach. He found a towel in the storage compartment and wrapped it around himself, turning on auto-pilot and slumping in the seat on his front. 

“You should sit properly,” Jaemin advised, swimming next to the boat. 

“I can’t,” was all Mark said in reply. He needed to take a hot shower and some painkillers, maybe. If he thought it was bad now, he was going to be _so_ sore tomorrow. But it was worth it. Jaemin was worth it.

He was almost sad when they returned to the docks. There was a tunnel that Jaemin could swim into that led to a pool inside the Institute, but it wasn’t anywhere near Mark’s bedroom. He climbed out of the boat and laid flat on the wood, letting the sun dry out his clothes as Jaemin popped up beside him, his smile beautiful and sad.

“I can stay out here,” Mark offered, but Jaemin shook his head.

“You need a shower, and rest,” Jaemin said, “and you should probably clean your prosthetic.” He reached for Mark’s artificial hand, gently tracing the frame. “You can come out after, though, if you’re feeling up to it.”

Mark frowned at the sky, where the sun was just beginning to set. Exhaustion was already settling into his bones, dragging him down. His eyelids felt heavy. “It’s almost dark.”

“I’ll be fine,” Jaemin replied, “I’m an apex predator, remember?”

Mark reached out and tenderly cupped Jaemin’s face, smiling softly when he leaned into his touch. “How could I forget?”

**Author's Note:**

> i'm going to hell ahahaha
> 
> btw we're going to pretend mark discovered a new species of white shark and named it carcharodon jaemin because romance <3
> 
> also jaehyun did clean mark's room while he was gone and mark gets teased for a solid month
> 
> thanks for reading! feel free to leave a kudos and comment if you enjoyed


End file.
